Year of Award

2022

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Cellular, Molecular and Microbial Biology

Department or School/College

Division of Biological Sciences

Committee Chair

D. Scott Samuels

Commitee Members

Dan Drecktrah, Michael Minnick, Stephen Lodmell, Angela Luis

Keywords

Borrelia, burgdorferi, hermsii

Abstract

Poly-N-acetylglucosamine (PNAG) is an extracellular polysaccharide consisting of β-1,6 N-acetylglucosamine monomers. PNAG is a key component of biofilms produced by diverse bacteria including Escherichia coli, Staphylococcus aureus, Yersinia pestis, Bacillus subtilis¸and many more. The structure of PNAG is highly conserved across the microbial world. Here, we demonstrate that PNAG is produced by two Borrelia species, Borrelia (Borreliella) burgdorferi and Borrelia hermsii. PNAG production in B. burgdorferi, the Lyme disease spirochete, depends on pngA (bb0620), a gene annotated to express a glycosyl hydrolase family 3 (GH3) enzyme, which is a novel pathway. Surprisingly, in B. burgdorferi, PNAG appears to be intracellular, most likely localizing to the periplasm, and plays a role in membrane structure. The B. burgdorferi null pngA mutant, which does not produce PNAG, has a dissemination phenotype in the mouse model of Lyme disease. Disruption of pngA also led to structural deformities and the appearance of bacteriophages on the cell surface. The ΔpngA mutant also showed a decrease in the ability to associate with host tick cells and to be phagocytosed by mouse macrophage-like cells. Disruption of PNAG production also led to some changes in the levels of cellular metabolites, including intermediates in glycerol metabolism. B. hermsii, the bacterial agent of tick-borne relapsing fever, produces PNAG in a similar manner to B. burgdorferi. The B. hermsii genome also contains a pngA ortholog that is required for PNAG production. PNAG production in B. hermsii plays a more substantial role in the mammalian immune response than what was observed in B. burgdorferi. The ability of the spirochetes to cause a classical febrile infection, including relapse, depended on PNAG. The ΔpngA mutant had a novel phenotype of a delayed infection in some mice after intraperitoneal injection. Infection with the ΔpngA mutant caused an increase in immune effector cells similar to what was seen in wild type; however, the ΔpngA mutant caused an increase in the number of splenic macrophages during infection and also increased expression of select immunoglobulins by the mouse. Therefore, in B. hermsii, PNAG may be playing a more immunomodulatory role compared to what was seen in B. burgdorferi and other bacterial pathogens. The data presented in this dissertation describe how Borreliaceae utilize PNAG in a novel, non-biofilm manner. We propose the name pngA (poly-N-acetylglucosamine A) for both bb0620 and bh0620 as the first gene involved in PNAG production identified in Borrelia species.

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